1. Field of the Invention
The present invention relates to improved polysilanes and to a novel process for the preparation of polysilanes and to the use of the final product polysilanes for the production of ceramic materials based on silicon carbide, whether in the form of coatings or matrices
2. Description of the Prior Art
EP-B-0,123,934 describes a process for the preparation of polysilanes comprising ethylene groups and hydrogen atoms bonded to silicon atoms, by reacting silane monomers such as CH.sub.3 (CH.sub.2 =CH)SiCl.sub.2, CH.sub.3 HSiCl.sub.2 and (CH.sub.3).sub.3 SiCl with sodium molten in an organic solvent.
According to this '934 patent, the simultaneous presence of ethylene groups and hydrogen atoms bonded to silicon atoms permits the crosslinking of the polymer by increasing the temperature, essentially without any loss in weight, such crosslinking facilitating conversion of the polysilanes into silicon carbide in a subsequent heat treatment.
The process of EP-B-0,123,934 also entails a sodium oxidation stage prior to the filtering of the reaction medium.
Such a stage makes it difficult to filter the reaction mixture. It thus becomes necessary to filter it several times after decantation in order to isolate the polymer.
Furthermore, the polymer obtained according to the process of EP-B-0,123,934 has a milky appearance, caused by washing it prior to filtration. This turbidity appears to be due to the formation of microgels in suspension in the polymer, which presents certain disadvantages, in particular on the experimental level (certain product analyses are difficult to carry out, for example analysis by gel permeation chromotography), as well as in the end use of the product, such as the impregnation of fine cavities with the polymer.